ML20050C301

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Safety Evaluation Supporting Amend 52 to License DPR-6
ML20050C301
Person / Time
Site: Big Rock Point File:Consumers Energy icon.png
Issue date: 04/02/1982
From:
Office of Nuclear Reactor Regulation
To:
Shared Package
ML20050C295 List:
References
NUDOCS 8204080386
Download: ML20050C301 (7)
v • d • e


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, UNITED STATES - 3,. - "

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NUCLEAR REGULATORY COMMISSION 3

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5AFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT N0. 52 TO FACILITY OPERATING LICENSE N0. OPR-6 CONSUMERS POWER COMPANY BIG ROCK POINT PLANT DOCKET NO. 50-155

1.0 INTRODUCTION

By. application dated September 18, 1981, as supplemented January 29, 1982, and March 10, 1982, Consumers Power Company (CPC) (the licensee) requested changes to the Technical Specifications appended to Facility Operating License No. DPR-6 for the. Big Rock Point Plant. The proposed changes would revise the reactor vessel pressure-temperature limits'. The changes presented in the March 10, 1982 letter were agreed to by the licensee after several discussions with the staff. The limits as revised are considered to be conservative by the licensee and the staff. The effective time period of 1.25 effective full power years was set to allow time for the licensee to gather more information to support less conservative limits for the longer term.

These revised limits for reactor vessel pressure and temperature are necessary to maintain the proper margin of safety against vessel failure due to embrittlement in the vessel beltline region from neutron exposure. Without an exemption to Section IV.A.2.c of

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Appendix G to 10 CFR Part 50, criticality would not have been allowed below approximately 200*F. Heat-up in the range of 200*F with pump heat alone is very slow and over a long period of time (several hours) might cause.the recirculation pumps to be damageddue to cavitation. Also, the lower temperature limit for criticality is based on the reference temperature of the flange region while the rest of the limits are based on shifts of the reference temperature of the beltline ragion. The reference temperature of the flange

. region does not shift since the neutron exposure of the flange region is insignificant. Therefore, an exemption to Sectibn IV.A.2.c of Appendix G to 10 CFR Part 50 was necessary to avoid the pump operational problem. The exemption reduces the lower temperature limit at which critica.lity is allowed to 120*F.

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i 2.0 EVALUATION The evaluation of reactor vessel pressure-tem'perature limits can be subdivided into three parts. First, the initial condition of the vessel metal in terms of RTNDT was estimated, where RTNDT"is the reference temperature of the beltline region of the vessel.

Second, how much the condition of the vessel metal has changed in B2040Go ME 820402

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DR ADOCK 0300p 55 PDR

l 20 years of operation in terms of RTNDT was estimated. These two components provide the present condition of the vessel metal.

Finally, the current rate of change of the condition of the vessel metal in terms of RTn was estimated. This permits the establishment of technically sound mits for the near future.

I Initial RThDT The initial RTNDT of the Big Rock Point reactor vessel was estimated

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by the staff to be -20*FT in the zone of interest, the ieactor beltline, the copper and nickel

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contents are as follows:,,'

1. Copper content - weld material - 0.27%

~ plate material - 0.10%

2. Nickel content'- weld material - 0.10%

plate material - 0.18%

The reactor wall is 5.25 inches thick at the beltline and the inside radius of the reactor vessel at the beltline is 53 inches.

The welds in the Big Rock Point vessel were made with ARCOS B-5 weld flux; at this time we have no generic data base giving the initial RT DT for welds made with that flux. Following the guidance of the N

Standard Review Plan one would estimate an initial RTNDT of 0*F for Big Rock Point, sinc'e no drop weight data are available for the ARCOS B-5 material. However, the licensee cited EPRI data as justification for a lower initial RTNDT. This EPRI data, actually presented in detail'in CEN-191 which is known as the C.E. thermal shock report, are for Linde 0091 weld flux and RACO-3 weld wire.

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From the information we have, the mean value of initial R7 DT for N

Linde 0091 flux welds is -56*F and the upper 26 value is -20*F.

Similar data for Linde 80 flux shows an upper 26 value of +20*F.

The typical upper shelf energy of welds from Linde 0091 f' lux is greater than 100 ft lb, whereas that of Linde 80 welds is about 70 ft lbs.

The upper shelf of ARCOS B-5 welds for Big Rock Point surveillance weld is about 93 ft lbs.

,Thernlydirect. data,forBigRockPointweldsare3Charpyhaluesat

+10 F, which gave energies of 50, 53.5 and 53.5 ft lbs and the sur-veillance weld for which the Charpy curve is shown in Figure 1.

As pointed out by the licensee, the 30 ft lb fix is about -70'F for the surveillance weld. Assuming the same shape curve, the 30 ft lb fix corresponding to the 3 Charpy value at +10 F would be about -40'F.

Based on these facts and the actual measured 50 ft lb level.of +10*F, we conclude that a conservative estimate for the' initial RTNDT is -20*F.

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Present RT mT We estimate that the RTNDT for the Big Rock Point reactor vessel is presently 155'F. Combined with an initial RTNDT of -20*F, we estimate to be 135'F. Figure 2 compares the surveillance the present RT NDT test results from Big Rock Point with the trend curves of Reg. Guide 1.99. Of particular interest are the two data points at a fluence of 2.3 x 1019 n/cmd showing a Charpy shift of 135 F for wall capsule 125 (reported in WCAP-9794, September 1980) and a. shift of 130*F for~an accelerated capsule reported earlier. These values are the same as that for a fluence of 7.1 x 1018 and are only moderately lower than the value of 170 - 230 degree F for a fluence of 1 x 1020 n/cm2 The com-parison shown in Figure 2 is consistent with recent findings that Reg.

Guide 1.99 overpredicts results for low nickel material quite signifi-

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cantly at high fluences.

Figure 3 compares the Big Rock Point surveillance data with low-nickel PWR surveillance data. The PWR surveillance data base has been fitted with a mean curve by multiple regression analysis with the following result:

ARTNDT = [.5 + 480 Cu + 270 CuN13 (f/lb ')

-[ There were 136 data points, and one standard deviation (one sigma) was 22*F.

The curve labeled "Guthrie Mean" in Figurd 3 is a plot of the above The Big Rock Point surveillance equation for 0.2g Cu and 0.1% nickel.n/cm2 and 135*F shift lies about one sigma data at 2.3 x 10 the predicted value of 158*F. The curve labeled "MPC mean" was i

developed from the data base available as of November 1977.

It does not have a nickel term, but is shown as a mean curve for the entire data base at the time it was drawn. Based on a comparison of the Big Rock Point data with these curves, we conclude that the Big Rock Point data cannot be used as the sole basis for the determination of Based on the Guthrie.mean trend curve for 0.27% Cu and 10% Ni, 4RTNDT.

we estimate that the present value of ARTNDT for Big Rock Point is 155*F. And using the estimated initial value of RTNDT of -20*F, we conclude that the present value of RTNDT for Big Rock Point is 135*F.

,Present Rate of Change of RTunT The CPC letter of March 10, 1982 stated that Table 4-1 is to be valid for 1.25 EFPY. The Guthrie curve and MPC curve from Figure 3 indicate that the RTNDT. value is presently increasing at a rate of 3-5*F per EFPY. The limits in the proposed Table 4-1 correspond to a RTNDT of 145'F, 10'F higher than the present RTNDT of 135'F. Therefore, the limits of the proposed Table 4-1 are acceptable for 1.25 EFPY.

4 e

4-i Criticality limit The criticality limit of 120'F given at bottom table 4-1 is acceptable based on the exemption to Appendix G of 10 CFR Part 50 included in this SE.

This limit is based on the reference temperature of the flange region; the rest of the l. imits in the table are based on shifts in the reference temperature of-the vessel beltline region.

The purpose of Section IV.A.2.c of Appendix G to 10 CFR Part 50 is to maintain the proper margin of safety against vessel failure in the flange region where bolt tension causes stresses-.on the metal.

The staff has conservatively calculated the appropriate 't'emperature to be 12a*F (RTNDT for the flange region + 60') to pr6 vide adequate protection at Big Rock Point. The flange region is not significantly affected by neutron exposure as in the beltline region.

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3.0 ENVIRONMENTAL CONSIDERATION

We have determined that the amendment does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact. Having made this determination, we have further concluded that the amendment invohss an action which is insignificant from the standpoint of. enviro.nmental impact and pursuant.to 10 CFR 551.5(d)(4) that an environmental impact statement or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of this amendment.

4.0 CONCLUSION

i We have concluded, based on the considerations discussed above,.that:

(1) because the amendment does not involve a.significant increase in the I

probability or consequences of accidents previously considered and does not involve a significant decrease in a safety margin, the amendment does t not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) such activities will be con-ducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defen'se and security or to the health and saf,ety of the public.

Attachments:

As stated

~Date:

April 2,1982 i

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